A variety of imaging systems have been proposed for use in equipment and on-board vehicles to monitor a driver and/or passenger(s) in an automotive vehicle. Some proposed imaging systems include one or more cameras focused on the operator or driver of the equipment or vehicle to capture images of the operator's or driver's face. The captured video images are processed to determine various facial characteristics of the eyes, face, and head. Given the determined facial characteristics, such as a driver's eye positioning and gaze, vehicle control systems can provide enhanced vehicle functions.
Many conventional approaches that employ active light illumination suffer from drawbacks. In particular, when an illuminated subject is wearing corrective lens eye glasses or sunglasses, the geometry (e.g., convex shape) of the glasses may reflect the light illuminated onto the image that is acquired by the imaging camera. This reflection of the illumination source is generally seen as a glare on the subject's glasses. The resultant glare may occur at the regions of interest near the eye(s) of the subject, thus inhibiting the ability to recognize imaged facial characteristics of the eyes, face, and head.
One approach that addresses the glare problem is disclosed in U.S. Pat. No. 7,646,422 entitled “Illumination and imaging system with glare reduction and method therefore.” The system disclosed in the aforementioned patent employs first and second light sources spaced from a centrally located video imaging camera and involves capturing successive images under illumination of different combinations of the light sources. A pixel-wise minimisation algorithm is performed on the sequence of images (such as an image pair) to produce a composite image in which glare is reduced.
Reduced glare images allow for enhanced imagery, which is particularly advantageous for use in a vehicle where an object driver of the vehicle may be wearing a corrective lens and glare may be present. Although the above described patent seems to solve some glare problems, it does not account for image motion between consecutive images. In a desired vehicle eye monitoring system, normal head movements should not result in interruption in monitoring the \ subject, operator or driver. As described in the above patent, when a driver's head or eye has moved between images and a pixel-wise “min” operation is performed on the images, then the resulting image may contain artifacts or ‘ghosting.’ These artifacts may totally negate the intended glare reduction effect which can be very detrimental to the analysis of the images. Ultimately, there will be a negative effect on the continuous operation and reliability of the above-described system. An improved method or system is needed to compensate for movement within the captured images, providing increased reliability of the on-board vehicle monitor systems. Given the determined facial characteristics, such as the operator's eye positioning and gaze, alternative vehicle or equipment control systems may provide higher safety and reliability levels for monitoring particular movements or behaviors.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.